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Impact of Warm Dark Matter on the Cosmic Neutrino Background Anisotropies

The Cosmic Neutrino Background (C$ν$B) anisotropies for massive neutrinos are a unique probe of large-scale structure formation. The redshift-distance measure is completely different for massive neutrinos as compared to electromagnetic radiation. The C$ν$B anisotropies in massive neutrinos grow in response to non-relativistic motion in gravitational potentials seeded by relatively high $k$-modes. Differences in the early phases of large-scale structure formation in Warm Dark Matter (WDM) versus Cold Dark Matter (CDM) cosmologies have an impact on the magnitude of the C$ν$B anisotropies for contributions to the angular power spectrum that peak at high $k$-modes. We take the examples of WDM consisting of 2, 3 or 7 keV sterile neutrinos and show that the C$ν$B anisotropies for 0.05 eV neutrinos drop off at high-$l$ multipole moment in the angular power spectrum relative to CDM. At the same angular scales that one can observe baryonic acoustical oscillations in the CMB, the C$ν$B anisotropies begin to become sensitive to differences in WDM and CDM cosmologies. The precision measurement of high-$l$ multipoles in the C$ν$B neutrino sky map is a potential possibility for the PTOLEMY experiment with thin film targets of spin-polarized atomic tritium superfluid that exhibit significant quantum liquid amplification for non-relativistic relic neutrino capture.